Ed Miliband has called on the prime minister to apologise for his NHS reforms after a critical report from a leading health thinktank described them as misguided and structurally incomprehensible.

The Labour leader, speaking on a visit to Stroud, in Gloucestershire, said the private sector should be a supplement to the public sector and not a substitute. He said: “David Cameron promised there would be no top-down reorganisation of the NHS and he broke that promise. Today the independent King’s Fund says that reorganisation has been disastrous for our NHS and damaged patient care.

“So now we know – every time patients wait longer for test results, longer in A&E and longer for an operation the responsibility goes directly to David Cameron’s door. Today he should personally apologise to the British people for betraying their trust, letting them down and damaging our National Health Service.”

In an assessment of the government’s NHS record, the King’s Fund said that the reorganisation forced through by then health secretary Andrew Lansley in the early period of the coalition was “damaging and distracting” for a health service that should have been preparing for the serious challenges it is now confronting.

Prof Chris Ham, the King’s Fund’s chief executive, said: “Historians will not be kind in their assessment of the coalition government’s record on NHS reform. The first three years were wasted on major organisational changes when the NHS should have been concentrating on growing financial and services pressures. This was a strategic error.”

As well as its unsparing critique of Lansley, the 80-page assessment of how the NHS has fared under the coalition also accuses Cameron of making errors that allowed Lansley to press ahead with a “sweeping and complicated” reorganisation of the NHS in England, even though the coalition agreement of May 2010 had specifically ruled one out.

When the health secretary unveiled the health and social care bill in autumn 2010, the influential thinktank’s report concludes that “information asymmetry in Whitehall enabled Lansley’s views to prevail [within the government]. There was no countervailing source of understanding of the NHS elsewhere in Whitehall, the prime minister having dismantled expertise built up by Tony Blair and Gordon Brown in No 10 as part of his drive to pass back power to departmental ministers.

“David Cameron’s failure to exercise due diligence on the reforms would come back to haunt him.”

The huge ensuing controversy – the largest generated by any changes in the NHS – pitted the medical establishment against the coalition. The outcry forced Cameron, in an unprecedented move, to call a “pause” in the bill’s passage and ask a group of experts, the NHS Future Forum, to improve it.

The King’s Fund also says that Lansley’s overhaul, which abolished hundreds of NHS bodies such as primary care trusts and strategic health authorities (SHA):

• Left the structure of the NHS so “complex, confusing and bureaucratic” that the organisation of the service “is not fit for purpose”.

• Wasted the time of NHS bosses, who were “distracted as they were required to rearrange the deckchairs rather than navigate safely past the iceberg” of growing demand for care and the service’s tightest-ever financial squeeze.

• Led to the loss of talented senior NHS leaders by creating an array of new organisations, each responsible for areas such as hospitals or public health, meaning that no one is in overall charge and the NHS now suffers from a leadership vacuum.

It also says that axing the 10 SHAs means that, despite the creation of 211 GP-led clinical commissioning groups, “nobody is in charge locally”, creating a huge risk, especially with the NHS having to undertake fresh changes now to the way it operates in order to remain viable.

But the thinktank’s most damaging criticism is its judgment that the huge disruption the bill unleashed has intensified the NHS’s growing problems in trying to treat patients in A&E or waiting for cancer care or a planned operation within set targets.

“By taking three years to dismantle the old structures and reassemble them into new ones, the government took scarce time and expertise away from efforts to address these [financial and service] pressures.

“Although it is not possible to demonstrate a causal relationship with NHS performance, it seems likely that the massive organisational changes that resulted from the reforms contributed to widespread financial distress and failure to hit key targets for patient care,” the report says.

Ham, one of a number of NHS experts who became part of a Downing Street health “kitchen cabinet” set up because of the controversy, said that “common sense would suggest” there was a link between the Bill and the NHS’s current difficulties.

Historians will not be kind in their assessment of the coalition government’s record on NHS reform

Prof Chris Ham

Stephen Dorrell, the former Tory health secretary who stood down last year as chair of the Commons health select committee, told the Observer that he agreed that the restructuring was the biggest mistake the coalition had made. “The reason I agree with it is partly for the political fallout, but the thing I care most about is the lost opportunity in the health and care system”, he said.

However, the thinktank also says that the Health and Social Care Act, despite increasing competition in the NHS, did not produce the widespread privatisation of NHS services that many critics feared. And it praises the Liberal Democrats, especially care services minister Norman Lamb, for ensuring progress on social care and mental health, and starting the integration of health and social care.

There was also some praise for Jeremy Hunt, who succeeded Lansley in September 2012, who the King’s Fund said had done much better by focusing on safety and quality of care.

Dr Mark Porter, leader of the British Medical Association, said the act had done “profound and intense” damage to the NHS because it prioritised competition over integration. “A BMA survey of doctors found that 95% did not believe the Act had improved the quality of services for patients, with three-quarters believing it has made the delivery of joined-up care more difficult.”

The department of health sidestepped the report’s many criticisms of Lansley’s tenure. Instead, in a short statement, a spokesman for Hunt welcomed “the King’s Fund’s recognition that the government’s focus on patient safety and integrated care is right for the NHS’s future”.

The department also claimed that Burnham’s plans to integrate health and social care as part of a 10-year NHS plan would involve yet another unpopular restructuring. “This independent assessment also puts paid to Ed Miliband’s myth that the reforms were about privatisation, and highlights why both the public and the health sector should be wary of Labour’s plans for upheaval and reorganisation”, he added.

Downing Street declined to comment last night and referred questions to the department of health.

Lansley defended his tenure. He said: “The report is silent on the question of whether patient care has been improved, on which the evidence is clear.

“When I was health secretary, year-long waiting times were eliminated, hospital infections dropped to their lowest levels ever, and thousands of lives were saved, and continue to be saved from improved care.

“The NHS is now judged to be the best health service in the world. The number of administrators has fallen, doctors and nurses have risen, productivity has gone up, and waste has been cut by over £5 billion a year.

“Public sector reform has never been a popularity contest, but these reforms will last. The independence of NHS England from national politicians and the leadership of local GP will stand the test of time, and patients will continue to see the results.”

Labour said the King’s Fund had borne out its criticisms at the time.

“Labour warned David Cameron that his reorganisation would damage the NHS and we now have independent authoritative evidence that that is what has happened”, said Andy Burnham, the shadow health secretary. “People will remember patients, nurses, doctors and midwives lining up in their thousands and pleading with the government to call it off. But they ploughed on and plunged the NHS into the chaos we see today”.